Without pretreatment, which membrane processes must be used to remove dissolved organic matter?

Without pretreatment, which membrane processes must be used to remove dissolved organic matter?

• A. Microfiltration and nanofiltration
• B. Nanofiltration and reverse osmosis
• C. Microfiltration and ultrafiltration
• D. Nanofiltration and ultrafiltration

Answer: (B)

Dissolved organic matter is composed of molecules that pass through many standard filter membranes, so you need membranes that can reject small dissolved solutes, not just particles. Microfiltration and ultrafiltration mainly remove suspended solids or very large molecules; a lot of dissolved organics can slip through because their sizes or charges aren’t enough to stop them. Nanofiltration membranes have tighter pore structures and can reject a substantial portion of larger organic molecules and some charged organics, while reversing osmosis membranes are even tighter and reject almost all dissolved substances, including small organic molecules. Using both together targets a wide range of DOM: NF handles larger or charged organics, and RO takes care of the smaller, uncharged ones that NF might miss. That combination is why nanofiltration and reverse osmosis are the appropriate choice for removing dissolved organic matter without pretreatment.

Dissolved organic matter is composed of molecules that pass through many standard filter membranes, so you need membranes that can reject small dissolved solutes, not just particles. Microfiltration and ultrafiltration mainly remove suspended solids or very large molecules; a lot of dissolved organics can slip through because their sizes or charges aren’t enough to stop them. Nanofiltration membranes have tighter pore structures and can reject a substantial portion of larger organic molecules and some charged organics, while reversing osmosis membranes are even tighter and reject almost all dissolved substances, including small organic molecules. Using both together targets a wide range of DOM: NF handles larger or charged organics, and RO takes care of the smaller, uncharged ones that NF might miss. That combination is why nanofiltration and reverse osmosis are the appropriate choice for removing dissolved organic matter without pretreatment.